Undelivered Mail Returned issue

Dear Team,
I created an e-mail server and tried sending, receiving, and working for one day. After that, this problem appeared to me. Is there a radical solution to this problem because I encountered it on more than one site?
Note:
PTR and DNS are ok

IMG_25541125×572 71.2 KB

IMG_25532143×386 128 KB

IMG_25551125×1934 252 KB

mail tester1882×682 126 KB

@ahmed1001 I have the same problem. Did you get the solution? How did you do it please?